The present invention relates to a motor control device and an electric power steering apparatus.
An electric power steering apparatus is known that aids a driver's steering operation by applying the drive force of a brushless motor to the steering mechanism of the vehicle. This electric power steering apparatus is provided with a rotation angle sensor that detects the value of a motor rotation angle, and a motor control device that controls the driving of the motor based on the detected value. In such a motor control device, if any abnormality occurs in the rotation angle sensor, the driving of the motor cannot be adequately controlled. As a measure for avoiding such a situation, a rotation angle sensorless control has been proposed, which is designed such that if abnormality occurs in the rotation angle sensor, the value of the motor rotation angle (electrical angle) is estimated based on the value of an induced voltage (counter-electromotive force) generated in the motor, and the driving of the motor is controlled based on the estimated value of the motor rotation angle. Japanese Laid-Open Patent Publication No. 2011-46251 discloses a motor control device that performs rotation angle sensorless control.
The motor control device described in Japanese Laid-Open Patent Publication No. 2011-46251 includes voltage detecting sections that detect the terminal voltages of respective phases of the motor, and a control section that controls the driving of the motor. The control section takes in the detection signals of the voltage detecting sections via separate signal lines. The control section calculates the detection values of the terminal voltages of respective phases of the motor based on the detection signals of the voltage detecting sections, and calculates the value of an induced voltage of the motor based on the calculated detection values. Subsequently, the control section estimates the value of a motor angular velocity based on the calculated induced voltage value, and calculates the change amount of the rotation angle per calculation cycle based on the calculation cycle and the estimated motor angular velocity value. The control section estimates the value of the present motor rotation angle by adding the calculated change amount in rotation angle to the motor rotation angle value estimated in the previous calculation cycle. Then, the control section controls the driving of the motor based on the estimated value of the present motor rotation angle.